1. Field of the Invention
The present invention relates to a mounting structure for a heat sink to an integrated circuit package.
2. Description of the Related Art
As an example of electronic devices demanded to have small sizes and high reliability, a portable electronic device such as a notebook personal computer has been widely spread on the market in recent years. High performance of such an electronic device requires the use of one or more integrated circuit package having a large heating value.
To ensure the radiation of the integrated circuit package having a large heating value, a heat sink is used in mounting the integrated circuit package on a printed wiring board. The heat sink is required to be mounted on a radiation surface of the integrated circuit package in securely close contact with each other, so as to prevent an increase in thermal resistance due to the contact. In relation with this, the optimization of a mounting structure of the heat sink to the integrated circuit package has been groped for.
FIGS. 16A and 16B are views for illustrating a conventional mounting structure of a heat sink to an integrated circuit package. Specifically, FIGS. 16A and 16B are a top plan view and an elevational view of the mounting structure. This mounting structure is disclosed in U.S. Pat. No. 5,099,550, for example. As shown in FIGS. 16A and 16B, an integrated circuit package 1 is mounted over a printed wiring board 3 with a small gap defined therebetween by soldering pins 2 of the integrated circuit package 1 to conductor patterns (not shown) of the printed wiring board 3. Recesses 6 are formed on upper edge portions of a heat sink 5 having radiating fins 4, and clips 7 each having a substantially C-shaped cross section are used to hold the heat sink 5 and the integrated circuit package 1 by engagement with the recesses 6 of the heat sink 5 and lower edge portions of the integrated circuit package 1.
FIG. 17 shows an elevational view of another conventional mounting structure. As similar to the structure shown in FIGS. 16A and 16B, an integrated circuit package 11 is mounted over a printed wiring board 13 by soldering pins 12 of the integrated circuit package 11 to conductor patterns (not shown) of the printed wiring board 13. Then, a heat sink 15 is fastened to the integrated circuit package 11 by fitting a leaf spring 16 on the heat sink 15 and then fixing the leaf spring 16 to the printed wiring board 13 by means of screws 17. A depressed portion 16a is formed at a substantially central portion of the leaf spring 16. The depressed portion 16a acts to press the heat sink 15, thereby bringing the heat sink 15 into close contact with the integrated circuit package 11.
In the prior art shown in FIGS. 16A and 16B, however, it is necessary to form the relatively large recesses 6 on the upper edge portions of the heat sink 5 because the upper edge portions must be held by the C-shaped clips 7. Accordingly, a radiation area on the heat sink 5 is reduced to cause a decrease in cooling efficiency.
On the other hand, in the prior art shown in FIG. 17, the leaf spring 16 must be fixed to the printed wiring board 13 by using a screwdriver. Accordingly, it is difficult for a user to easily replace the integrated circuit package 11.